1. Field of the Invention
The present invention relates to a head slider capable of suppressing the variation and irregularity of flying height, or the variation of contact pressure, and a recording-and-reproducing apparatus provided with such a head slider for supporting a read/write head at a low flying height or supporting a read/write head in small-force, stable contact with a recording medium to enable recording at a high recording density.
2. Description of the Related Art
Active efforts have been made in recent years for the development of techniques necessary to achieve high-density recording by recording-and-reproducing apparatus. Attempts to increase both bit density (recording density with respect to a circumferential direction of a disk) and track density (recording density with respect to the radial direction of a disk) have been made to increase recording density when recording information by a magnetic disk recording-and-reproducing apparatus. The reduction of the flying height of a head slider (hereinafter referred to simply as "slider") supporting a read/write head (hereinafter referred to simply as "head") is essential to increasing bit density. However, the flying height of a conventional slider is subject to dynamic variation during a seek operation, which is an obstacle to the reduction of the flying height of the conventional slider. Causes of the dynamic variation of the flying height of the current slider will be described below.
FIG. 19 schematically shows a magnetic disk drive provided with a general slider 101. Positional flying height difference, i.e., the difference between the flying height of the slider 101, typically, a taper flat slider, when the slider 101 is at a position corresponding to an inner peripheral portion of a disk 102, i.e., an information recording medium, and that of the same when the slider 101 is at a position corresponding to an outer peripheral portion of the disk 102, is suppressed, in most cases, by using the yaw angle dependence of flying height. Yaw angle is the angle .theta. between the direction of rotation of the disk and the longitudinal axis of the slider 101. As shown in FIG. 19, in a general magnetic disk drive, an actuator 103 for positioning a head is disposed relative to the disk 102 so that the yaw angle is small when the slider 102 is in an inner peripheral portion X of the disk 102, and large when the slider 102 is in an outer peripheral portion Y of the same.
Referring to FIG. 21 showing the taper flat slider 101 in a schematic perspective view, the taper flat slider 101 has elongate dynamic pressure generating parts 101a extending in the rotating direction A of the disk 102, i.e., a direction in which the disk 102 rotates relative to the longitudinal axis of the slider 101. The slider 101 is kept flying over the disk 102 by dynamic pressures generated in spaces between the dynamic pressure generating parts 101a and the rotating disk 102. The pressure generating efficiency of the dynamic pressure generating parts 101a extending in the rotating direction A of the disk is reduced when the rotating direction A of the disk relative to the slider changes to a rotating direction B relative to the disk due to the yawing of the slider at a yaw angle relative to the rotating direction A. Whereas air currents flow through a relatively long entire length of the slider from the front end of the same and contributes effectively to the generation of dynamic pressure when the yaw angle of the slider is relatively small, part of the air current flows obliquely from the front end of the slider and leaves the slider from the side edge of the same, another part of the air current flows obliquely from the side edge of the slider and leaves the slider from the back end of the same and hence air currents are unable to flow through a distance necessary for generating an effective dynamic pressure when the yaw angle of the slider is relatively large. Such a flow of air currents oblique to the slider is called air current leakage. Therefore, when the yaw angle of the prior art taper flat slider 101 increases as the taper flat slider 101 moves toward the outer peripheral protion Y of the disk, the dynamic pressure generating efficiency decreases. Consequently, the hydrodynamic force acting on the slider 101 does not vary because when the slider 101 moves toward the outer peripheral portion Y of the disk where the circumferential speed is higher than that in the inner peripheral portion X and hence the positional variation of the flying height of the slider 101 can be suppressed.
Incidentally, the disk 102 has a circumferential speed component V.sub.r (5 to 10 m/s), i.e., a circumferential speed relative to the slider 102, and, when the slider 102 is moved for a seek operation, a seek speed component V.sub.s (about 1 m/s at a maximum), i.e., a radial speed relative to the slider 102, perpendicular to the circumferential speed V.sub.r as shown in FIG. 20. Therefore, the direction of the resultant vector V of the circumferential speed component V.sub.r and the seek speed component V.sub.s is inclined at an angle in the range of 5.degree. to 10.degree. to the longitudinal axis of the slider 101. Therefore, an equivalent yaw angle change .theta.' is added to the yaw angle of the slider 102 during the seek operation. Since the dynamic pressure generating efficiency is reduced during the seek operation due to the transverse leakage of air currents from the dynamic pressure generating parts 101a during the seek operation on the same principle as that of yaw angle dependence as explained with reference to FIG. 21, transient flying height reduction occurs. It has been verified through experiments that, in general, the magnitude of transient flying height reduction is greater than 10 nm. Therefore, the space between the slider 101 and the disk 102 in an on-tracking state must be determined allowing for an allowance for the flying height reduction in a seeking state. Such a yaw-angle-dependent variation of the flying height is a significant factor that obstructs the reduction of the flying height.
A contact recording technique has been examined with an intention to further increase recording density. The contact recording technique sets a head in contact with a disk 102 so that the flying height is substantially zero. The reduction of abrasion of the head is the most important technical problem in the contact recording technique. The contact force between the head and the disk must be low and stable to reduce the abrasion of the head. However, as mentioned above, the contact force between the current slider 101 and the disk 102 varies with the variation of the equivalent yaw angle and hence it is impossible to maintain a low, stable contact force between the slider 101 and the disk 102. When the head is abraded greatly, a contact part of the head to be kept in contact with the disk 102 may possibly be spaced from the surface of the disk 102 when the flying height of the slider 101 changes between the inner peripheral portion and the outer peripheral portion of the disk 102.
When a head provided with a magnetoresistance-effect device, i.e., an MR head which has recently been applied to practical uses and is expected to be prevalently used in the future, is employed, a recording-and-reproducing apparatus needs a write head and a read head. Generally, the two heads are arranged in the direction of arrangement of tracks. In such a configuration, the two heads are dislocated relative to each other in the direction of the width of tracks (tracking dislocation) when the yaw angle changes greatly between the inner peripheral portion and the outer peripheral portion of the disk. A method intended to solve such a problem employs a linear actuator, and another method proposed in JP-A No. 5-298615 employs an actuator arm having an appropriate length to reduce the variation of the yaw angle. Therefore, it is highly possible that a method of suppressing the variation of the flying height without using the yaw angle dependence is necessary for a slider supporting an MR head.
As explained above, the conventional slider 10 utilizes yaw angle dependence to reduce the positional flying height difference. Consequently, the flying height is reduced or the contact force varies due to the equivalent yaw angle variation during the seek operation. Accordingly, it is difficult to reduce the flying height of the head or to keep the head in contact with the disk at a low, stable contact pressure. When the head is abraded excessively by the contact recording operation and the flying position of the head varies between the inner peripheral portion and the outer peripheral portion of the disk 102, it is possible that the contact part of the head is separated from the surface of the disk 102 and a space is formed between the contact part of the head and the surface of the disk 102. Moreover, a slider supporting an MR head requires a method of reducing the positional flying height difference without using yaw angle dependence.